Gu Yong (onyomi: Ko Yō) is a student of Cai Yong and an official of Sun Quan. Known for his personal conduct, he became Chancellor of Wu shortly after his lord declared himself emperor, especially to take control of decisions whenever Sun Quan's judgment was clouded from being drunk.

Born in Wu county in Wu prefecture, Gu Yong was a member of the Gu family, one of the four illustrious houses of Wu. When Cai Yong fled south to escape the wrath of the eunuchs, he met Gu who became Cai's student for calligraphy and classics. After his tutelage, Gu Yong would become the governor of multiple prefectures in Yang Province, and ensured the prefecture's stability during his tenure. He would later be an integral factor in helping the capable Zhang Wen rise to power in Wu.

In 229, Sun Quan distanced himself from Cao Pi of Wei by declaring himself emperor; Gu Yong would become chancellor shortly afterwards. As he was known for remaining quiet whenever he disapproved of something, Sun Quan would often test theories and potential policies on Gu to see if everything was in order. If Gu did not respond, Sun would have the papers reviewed once more.

Gu Yong was well-known for upholding proper conduct wherever he went, speaking with confidence and reason. His refusal to drink also earned him the respect and fear of his colleagues. Not one to hold grudges or act out of spite, he only punished his enemies in accordance to the law as in the case with Lu Yi, a corrupt official who maligned others including Gu Yong. When Lu Yi's crimes were revealed to all, Gu Yong was appointed as his judge. Contrary to what others expected, he remained objective during the trial and reprimanded fellow victim Huai Xu for cursing at their oppressor, saying "The state has laws, it is not necessary for you to do that." In 243, Gu Yong died from illness and was succeeded by Lu Xun. He was also posthumously honored as Marquis Su.

Gu Yong is first mentioned in the novel as one of Zhang Hong's friends and becomes a deputy governor with the latter's recommendation. When Zhuge Liang comes to Wu seeking an alliance against Cao Cao, he joins the other scholars in debating with the strategist, being among those who oppose resistance against Cao Cao.

Despite his opposition, Sun Quan ultimately decides to resist. As a result, the Sun-Liu alliance successfully defeats Cao Cao at Chibi. At this point, the issue of Jingzhou comes to light, and Liu Bei, who had just married Lady Sun, leaves for Yizhou to visit his relative Liu Zhang. During Liu Bei's absence, Gu Yong recommends that Sun Quan launch an attack at Jingzhou while Liu Bei is away, but the idea is scrapped when Lady Wu hears of it and scolds her son for not showing concern for his sister.

Later, Gu Yong appears with Zhang Zhao when Liu Bei takes Liu Zhang's land, and the two advise Sun Quan to "torture" Zhuge Jin's family in order to get back the land at Jingzhou through Zhuge Liang. However, the plan later fails due to Guan Yu's refusal to comply with Zhuge Liang's letter to return the portion of the province. Shortly before Guan Yu's assault on Fancheng, a messenger from Cao Cao arrives proposing a joint assault while Guan Yu is busy, and Gu Yong supported the proposal of a joint attack. Guan Yu's refusal to betroth his daughter to Sun Quan's son and insulting remarks eventually convince Sun Quan to join Cao Cao's attack.

Soon after Guan Yu's death at Maicheng, Liu Bei launches a punitive expedition against Wu. Gu Yong and the other officials are hesitant in relying on Lu Xun for this campaign, but their doubts are eased when the young tactician overwhelms Liu Bei at Yiling with a fire attack. Shortly before the battle, Cao Pi offers princely titles to Sun Quan. Gu Yong vehemently opposes the decision to accept them, but Sun Quan goes against him, citing how Liu Bang once accepted a title from Xiang Yu.

Once Liu Bei dies, Cao Pi sends a messenger to Wu requesting an assault force in a joint attack against Shu. Both Gu Yong and Zhang Zhao tell to Sun Quan to consult Lu Xun first on this matter, the former having acknowledged the younger officer's capabilities. Following Lu Xun's advice, Sun Quan feigns inability to immediately attack and does not send an army to answer Wei's call, thus maintaining good relations with Shu. When Cao Xiu leads an attack at Shiting, Gu Yong recommends Lu Xun once more to deal with this threat. Some time after Cao Xiu's defeat, Sun Quan becomes Emperor of Wu with Gu Yong as his prime minister.